1. Please double-check the registration status of both FMC appliances to ensure they are indeed registered and in service. Make sure that both appliances are connected to the network and reachable.
2. Ensure that the FMC synchronization between the two appliances is functioning correctly. If there are any synchronization issues or delays, it can lead to misleading error messages. Check the synchronization settings and logs to identify any potential problems.
3. Try restarting both FMC appliances to ensure they are in a clean state before starting the upgrade process. This can help clear any temporary issues or stuck processes that might be causing the error.
Remember to exercise caution when performing any system changes or upgrades, and always ensure you have a backup of your configuration and data before proceeding.
If the problem exists, you can open case to Cisco support for further troubleshooting.
